Seamark Nunn Ok deck removal

share hints, tips and experiences
Post Reply
Pike
Posts: 36
Joined: Tue Dec 06, 2011 2:08 pm
Location: Bedfordshire

Seamark Nunn Ok deck removal

Post by Pike »

I've just acquired a mid 70's Seamark Nunn Ok Grp dinghy that needs a few jobs doing below the deck (new fwd bulkhead and mast step repair) and was wondering if anybody had any experience of removing the deck on one of these? It appears that it is just attached with a load of screws around the gunwhales and cockpit, along with some kind of sealant that appears to be in poor condition.
Thanks
Andy
bornagainmothie
Posts: 222
Joined: Mon Apr 23, 2012 1:28 pm

Re: Seamark Nunn Ok deck removal

Post by bornagainmothie »

Most GRP hulls of that era were 2 or more mouldings joined up with a bit of sealant and screws. With the age of the sealant now, they don't put up much of a fight to seperate as long as you have found all the fixings and work carefully around to open up the gap with a wide chisel or scraper. A bit of warming with a heat gun may help if there is resin in the joints.

I would take a good look at some more modern versions and think about adding some bulkheads and stiffening inside while the decks are off. Because of the simple top and bottom moulding used there is often only one buoyancy compartment, which is not clever especially if its not airtight.

To reassemble the mouldings a much stronger join can be made by using epoxy resin and microfibres/balloons to help fill any gaps.
Pike
Posts: 36
Joined: Tue Dec 06, 2011 2:08 pm
Location: Bedfordshire

Re: Seamark Nunn Ok deck removal

Post by Pike »

The deck is off now, only took about an hour with barely any resistance from around the edges once the screws were removed. Area
around centre board case put up a bit of a fight but the tip to use a heat gun worked well.

New fwd bulkhead now fitted along with drain tube back to the cockpit.

Next job before deck goes back on is to repair the mast step as the wooden block that is bonded into the hull and glassed over is totally
saturated with water. Not sure whether to replace with a new piece of wood (got a few pieces of oak that might be suitable)
or use something else.
JimC
Posts: 1721
Joined: Sun Oct 03, 2004 10:24 pm
Location: Surrey
Contact:

Re: Seamark Nunn Ok deck removal

Post by JimC »

Pike wrote:or use something else.
I'd use something else. If you can get an offcut of high density foam core from a hightech boatbuilder that would be perfect. Similar mechanical properties and weight to wood, but won't rot and won't trap water. Failing that maybe nylon chopping board?
Pike
Posts: 36
Joined: Tue Dec 06, 2011 2:08 pm
Location: Bedfordshire

Re: Seamark Nunn Ok deck removal

Post by Pike »

Jim,

Is it possible to successfully bond bolts into the foam?
Previously the mast step had a wooden block sitting on the keel line with a cross brace at either end which each had a bolt fitted head down. Then a big plate of 1/2" tufnol was sat on top to function as an adjustable lower bearing, held on by wing nuts fitted to the bolts.

Thanks
Andy
JimC
Posts: 1721
Joined: Sun Oct 03, 2004 10:24 pm
Location: Surrey
Contact:

Re: Seamark Nunn Ok deck removal

Post by JimC »

The high density foam will take screws pretty much as well as wood will. I have successfully buried hex bolt heads in a high microfibre epoxy fill, but I was pretty desperate.
If you want to replicate that original setup (and I might be more inclined to see what current best practice is in the OK class and go that way) I think I would consider fabricating a carbon plate a few mm thick or a glass plate several mm thick off the boat, and put longish machine screws through it and bolt the screws onto it firmly in place with penny washers each side and nyloc nuts. Then I'd thoroughly bond and glass that assembly in place so it can never move, the bolt heads disappearing into filler, and add a spacer, which might well be nylon board on top of that to hide the nuts with the bolt ends projecting through and also get you up to the same height as the original setup. Then you could have your tufnol and wing nuts on top. Arguably the thicker glass plate would be better since there'd be no electrochemical possibilities.
Post Reply